Coloration of hair is a procedure practiced from antiquity employing a variety of means. In modern times, the most extensively used method employed to color hair is to color hair by an oxidative dyeing process employing hair coloring systems utilizing one or more oxidative hair coloring agents in combination with one or more oxidizing agents.
Most commonly a peroxy oxidizing agent is used in combination with one or more oxidative hair coloring agents, generally small molecules capable of diffusing into hair and comprising one or more primary intermediates and one or more couplers. In this procedure, a peroxide material, such as hydrogen peroxide, is employed to activate the small molecules of primary intermediates and couplers so that they react to form larger sized complexes in the hair shaft to color the hair in a variety of shades and colors.
Hydrogen peroxide is the most commonly used oxidizing agent employed for oxidative hair dyeing. However, while hydrogen peroxide is the most commonly used oxidizing agent for oxidative coloring of hair, the use of hydrogen peroxide is not without its drawbacks and undesirable characteristics. For example, hydrogen peroxide treatment of hair can solubilize the colored melanin component in hair causing undesirable bleaching of the hair. Moreover, the action of hydrogen peroxide on hair can produce damage to the hair resulting in brittleness and other poor qualities of the hair.
A further drawback in the use of hydrogen peroxide as an oxidizing agent for oxidative dyeing of hair is the requirement for a high pH of above pH 9 for an extended period of time of up to 30 to 60 minutes for the hydrogen peroxide to be in contact with the hair and other dye composition components in order to produce the most effective oxidization of the dye components. While the hydrogen peroxide can be employed at lower pH conditions, oxidation of the dye components and coloration of the hair is generally not as effective.
Additionally, a further drawback is that hydrogen peroxide is a rather unstable liquid requiring special handling and packaging.
In International Application Publication Nos. WO 97/24105, WO 97/24106, WO 97/24107 and WO 98/27943 of the Proctor & Gamble Company, there are proposals for use of organic peroxyacids or precursors therefor as oxidizing agents in hair coloring compositions. However, many of these organic oxidizing agents are liquids that are explosive in nature, not as effective as hydrogen peroxide, and have other drawbacks.